Atrial fibrillation is a heart rhythm abnormality that is one of the leading causes of cardiovascular disease-related morbidity in the world. Clinically, atrial fibrillation involves an abnormality of electrical impulse formation and conduction that originates in the atria, that is, the upper chambers of the heart. Atrial fibrillation can occur in patients with any type of underlying structural heart abnormality, such as coronary artery disease, valvular heart disease, congenital heart disease, and cardiomyopathies of various kinds, thereby complicating patient management and therapy. Further, atrial fibrillation can sometimes occur in patients with no known underlying structural abnormalities or in patients with lung disease or hormonal or metabolic disorders. As well, the occurrence of atrial fibrillation can exacerbate other disorders, for example, myocardial ischemia or congestive heart failure. Effective treatment must include weighing the presence of any comorbidities primary or secondary to atrial fibrillation and whether therapy should be directed against rate control or restoration of normal sinus rhythm.
Atrial fibrillation is characterized by multiple swirling wavelets of electrical current spreading across the atria in a disorganized manner. The irregularity of electrical conduction throughout the atria creates irregular impulse propagation through the atrioventricular node into the ventricle and can frequently cause a patient to notice a disturbingly erratic sensation of the heartbeat. These symptoms of an erratic heartbeat, or palpitation, can be trivial or seriously disturbing to the patient's daily functions. Occasionally, the impulse conduction is extremely rapid, leading to reduced diastolic filling of the heart chambers and reduced cardiac pumping action. Rapid heart rate, as well as poor coordination of atrial and ventricular pumping functions, not only lead to a decrease in cardiac output, but also, depending upon the nature of any underlying heart disease, can exacerbate heart failure, coronary blood flow, and pulmonary disorders. Atrial fibrillation may also occur and be totally inconsequential in its cardiovascular and cardiopulmonary consequences or its affect on the patient's quality of life. Yet, even if silent from a cardiovascular and symptom perspective, if persisting beyond a 48 hour period, atrial fibrillation can also result in blood clot formation in the atria, thereby creating the potential for thromboembolism which can lead to strokes or injuries to limbs and major organs. Thus, the outcomes or consequences of atrial fibrillation can be gross or subtle and be rapid or gradual in onset, consequently requiring a range of approaches, from observation to providing emergent interventions.
The early diagnosis, prevention and monitoring of the consequences of atrial fibrillation can be relatively difficult. First, atrial fibrillation onset runs an erratic, unpredictable course and is generally silent and undetectable to the patient. More often, atrial fibrillation either results in no symptoms at least for some period of time early in the course of onset, or in fatigue or difficulties in breathing usually in the case of those patients having comorbid conditions. Occasionally, a patient will have no complaints but will unconsciously compensate by limiting his or her daily activities. Sometimes, the consequences of atrial fibrillation are more overt. In any case, fatigue or difficulty breathing is often a consequence of atrial fibrillation complicating the pathophysiology of coexisting conditions of congestive heart failure, myocardial ischemia, and/or respiratory insufficiency, for example.
The susceptibility to suffer from atrial fibrillation depends upon the patient's age, gender, physical condition, presence or absence of heart failure, coronary artery disease, lung disease, and the incidence of other factors, such as diabetes, lung disease, high blood pressure, anemia and kidney function. No one factor is dispositive. Evaluations for atrial fibrillation and its consequences, with annual or even monthly checkups, provide, at best, a “snapshot” of patient wellness and the incremental and subtle clinicophysiological changes which portend the onset or progression of atrial fibrillation often go unnoticed, unless electrocardiographic documentation is obtained and simultaneously correlated with cardiovascular and cardiopulmonary physiological measures. Documentation of improvements following initiation of therapy can be equally elusive.
Nevertheless, taking advantage of frequently and regularly measured physiological measures, such as recorded manually by a patient, via an external monitoring or therapeutic device, or via implantable device technologies, can provide a degree of detection, treatment and prevention heretofore unknown. In addition, monitoring of the physiological consequences of the onset and offset of atrial fibrillation can provide invaluable guidance in directing when and what therapeutic intervention is most appropriate, particularly when atrial fibrillation is coupled with other comorbidities. For instance, patients already suffering from some form of treatable heart disease often receive an implantable pulse generator (IPG), cardiovascular or arrhythmia monitor, therapeutic device, or similar external wearable device, with which rhythm and structural problems of the heart can be monitored and treated. These types of devices are useful for detecting physiological changes in patient conditions through the retrieval and analysis of telemetered signals stored in an on-board, volatile memory. Typically, these devices can store more than thirty minutes of per heartbeat data recorded on a per heartbeat, binned average basis, or on a derived basis from, for example, extensive data regarding atrial or ventricular electrical activity, minute ventilation, patient activity score, cardiac output score, mixed venous oxygen score, cardiovascular pressure measures, and the like. However, the proper analysis of retrieved telemetered signals requires detailed medical subspecialty knowledge, particularly by cardiologists and cardiac electrophysiologists.
Alternatively, these telemetered signals can be remotely collected and analyzed using an automated patient care system. One such system is described in a related, commonly owned U.S. Pat. No. 6,312,378, issued Nov. 6, 2001, the disclosure of which is incorporated herein by reference. A medical device adapted to be implanted in an individual patient records telemetered signals that are then retrieved on a regular, periodic basis using an interrogator or similar interfacing device. The telemetered signals are downloaded via an internetwork onto a network server on a regular, e.g., daily, basis and stored as sets of collected measures in a database along with other patient care records. The information is then analyzed in an automated fashion and feedback, which includes a patient status indicator, is provided to the patient.
While such an automated system can serve as a valuable tool in providing remote patient care, an approach to systematically correlating and analyzing the raw collected telemetered signals, as well as manually collected physiological measures, through applied cardiovascular medical knowledge to accurately diagnose the consequences of the onset of a particular medical condition, such as atrial fibrillation, is needed. One automated patient care system directed to a patient-specific monitoring function, albeit focused on ventricular rather than atrial arrhythmias, is described in U.S. Pat. No. 5,113,869 ('869) to Nappholz et al. The '869 patent discloses an implantable, programmable electrocardiography (ECG) patient monitoring device that senses and analyzes ECG signals to detect ECG and physiological signal characteristics predictive of malignant cardiac arrhythmias. The monitoring device can communicate a warning signal to an external device when arrhythmias are predicted. However, the Nappholz device is limited to detecting tachycardias. Unlike requirements for automated monitoring of the consequences of atrial fibrillation, the Nappholz device focuses on rudimentary ECG signals indicative of malignant cardiac tachycardias, an already well-established technique that can be readily used with on-board signal detection techniques. Also, the Nappholz device is patient specific only and is unable to automatically take into consideration a broader patient or peer group history for reference to detect and consider the progression or improvement of cardiovascular disease. Moreover, the Nappholz device has a limited capability to automatically self-reference multiple data points in time and cannot detect disease regression even in the individual patient. In addition, the Nappholz device must be implanted and cannot function as an external monitor. Also, the Nappholz device neither monitors nor treats the cardiovascular and cardiopulmonary consequences of atrial fibrillation.
More specifically, the diagnosis and treatment of atrial fibrillation using implantable anti-arrhythmia devices has been widely addressed in the prior art and is described, for example, in U.S. Pat. No. 5,931,857 ('857) to Prieve et al. and U.S. Pat. No. 5,855,593 ('593) to Olson et al. The '857 patent discloses an implantable device which continuously monitors for tachyarrhythmia conditions and an associated patient activator. Two sets of arrhythmia detection criteria are utilized for evaluating autonomous and patient-activated anti-arrhythmia therapy. The '593 patent discloses a device capable of arrhythmia detection and classification based on a set of prioritized rules. However, both the Prieve and Olson devices are directed to diagnosing and treating the arrhythmias in isolation without detailed consideration of coexisting conditions and the cardiovascular and cardiopulmonary consequences of those disorders.
As a result, there is a need for a systematic approach to detecting trends in regularly collected physiological data indicative of the onset, progression, regression, or status quo of atrial fibrillation diagnosed and monitored using an automated, remote patient care system, such need being particularly heightened in the presence of comorbidities, such as congestive heart failure, myocardial ischemia, respiratory insufficiency, and related disorders. The physiological data could be telemetered signals data recorded either by an external or an implantable medical device or, alternatively, individual measures collected through manual means. Preferably, such an approach would be capable of diagnosing the cardiovascular and cardiopulmonary consequences of both acute and chronic atrial fibrillation conditions, as well as the symptoms of other cardiovascular diseases. In addition, findings from individual, peer group, and general population patient care records could be integrated into continuous, on-going monitoring and analysis.